Presentation on theme: "PRINCIPLES OF BIOCHEMISTRY"— Presentation transcript:
1PRINCIPLES OF BIOCHEMISTRY BCM 3000PRINCIPLES OF BIOCHEMISTRY(Semester /12)
2LIPID Learning outcome (Objectives) Function and distribution. Characteristics of fatty acids-structure and chemical properties.Saturated and unsaturated fatty acids .Structures and properties of phospholipids, sphingolipids, waxes, terpenes and steroids.
7LIPID Fat : Triglycerides in the form of solids at room temperature DEFINITION : General definition – all compounds called fat and oilsTECHNICAL DEFINITIONFat : Triglycerides in the form of solids at room temperatureOils : Triglycerides which are liquid at room temperature
8General DefinitionAny natural compound which is insoluble or nearly insoluble in water but soluble in non-polar solvents –ChloroformCS2Etherwarm orhot ethanol
9FUNCTIONSLipids are widely distributed in both animal and plant systems and perform a wide variety of functionsStructural functions - Components of membranesStorage forms of carbon and energyprecursor for major compounds – e.g. hormones.Insulators - thermal, electrical or physical shockprotective coatings – prevent infections, loss or addition of compoundsRegulators - as vitamins & hormones
17FATTY ACIDSLong chain aliphatic carboxylic acids- contains carboxyl group – polar head and `tail’ containing hydrocarbon chainAmphiphilic compounds – hydrophilic head and hydrophobic tailCOOH can be ionisedMonocarboxyilic acids – linear hydrocarbon chain, even carbon numbers – between C12-C20Short, longer , branched, cyclic and odd numbers also exist BUT not many
20Structure of Fatty Acids - Saturated Fatsmostly from animal sources,have all single bonds between the carbons in their fatty acid tails, thus all the carbons are also bonded to the maximum number of hydrogens possible.saturated fatsThe hydrocarbon chains in these fatty acids are, thus, fairly straight and can pack closely together, making these fats solid at room temperature.
24Unsaturated fatty acids C=C double bond arranged in two waysIn cis bonds, the two pieces of the carbon chain on either side of the double bond are either both “up” or both “down,” such that both are on the same side of the moleculeIn trans bonds, the two pieces of the molecule are on opposite sides of the double bond, that is, one “up” and one “down” across from each otherNaturally-occurring unsaturated vegetable oils have almost all cis bonds, but using oil for frying causes some of the cis bonds to convert to trans bonds
28fatty acids with trans bonds are carcinogenic, or cancer-causing. containing products such as margarine are quite high,
29Oils mostly from plant sources, have some double bonds between some of the carbons in the hydrocarbon tail, causing bends or “kinks” in the shape of the molecules.Because some of the carbons share double bonds, they’re not bonded to as many hydrogensoils are called unsaturated fats.kinks unsaturated fats can’t pack as closely together, making them liquid at room temperature
32Making margarineVegetable oils often contain high proportions of polyunsaturated and mono-unsaturated fats (oils) liquids at room temperature.You can "harden" (raise the melting point of) the oil by hydrogenating it in the presence of a nickel catalyst.
42Triacylglycerol – the most abundant No ionic groups - neutral lipidsTriacylglycerol = neutral fats neutral oils (liquid)
43FUNCTIONS IN ANIMALSAdipose tissues - `fat depots' = storage forms of carbon and energyII. Transport - chylomicrons - = lipoprotein – fatty acids are transported through lymphatic system and blood tissue adipose tissues and other organsIII. `Physical protection' - e.g. temperature.
55Base Hydrolysis = SAPONIFICATION (i.) Base Hydrolysis Fatty acid + Glycerol or Salts of fatty acid + Glycerolinside cells – by enzymes (lipase) – very specific for ester bonds – products are glycerol + fatty acidsNon-enzymatic- with alkali (base) salts of fatty acid + Glycerolsalts of fatty acids = soapBase Hydrolysis = SAPONIFICATION
56SAPONIFICATIONThe reaction of triacylglycerol with base (alkali) - e.g.. NaOH, KOHTriacylglycerol – presence of strong ester bondEster bond can be hydrolyzed by base salts of fatty acid + glycerolSalts = soap – react as a soap/detergent
60Detergent? =`surface active agents' – lower surface tension of surface of water H2O = `poor cleansing agent - Y? Because the molecule is very polar and tend to stick to each other – therefore cannot enter non-polar areas like grease, oil, dirt
61HOW DOES A DETERGENT WORK ?? Hydrophobic tails enters grease layersii. Hydrophilic heads come into contact with aqueous layer separate grease layer from the surfaceSmall grease globules form- `pincushion‘These globules have similar charges - therefore cannot go near each other – can wash
65Best detergent strong hydrophilic and hydrophobic tail Ordinary soap = mixture of potassium salts of fatty acids from saponification - not a very good detergent ? e.g. Sodium palmitateThe negative ions in soap forms precipitate with metals in hard water (?) use syndets = soluble in watere.g.. SDS = Sodium dodecil sulfate
684. RANCIDITYExpose triacylglycerol to warm and moist air rancid (tengik)2 reactions take placeEster hydrolysisOxidation of the double bondsHydrolysis - water (inside the lipid) + enzyme (bacteria in the air)Oxidation-by O2 on the side chain of triacylglycerol short chain fatty acids – rancid (tengik)
74Phosphoglycerides can be further esterified to form other lipids Phosphatidylcholine ( choline ester)Phosphatidylethanolamine (ethanolamine)Phosphatidylserine (serine) All are important components of membranes
80SPHINGOLIPID No glycerol – replaced with amine alcohol = Sphingosine Number of carbon atoms –variesThe simplest = ceramides = Fatty acid + sphingosine through amino group via amide bondSphingomyelin – an example of sphingolipid - 1o alcohol esterified to phosphate amino alcohol (= choline)Found in nerve membranes and brain
81SPHINGOLIPID CHCH(CH2)12CH3 H2C OH CHOH H2COH CH NH2 CH2OH What is the main structure for sphingolipid?SphingosineDraw the structure of sphingosineDraw the structure of glycerol and compare between the twoCHCH(CH2)12CH3CHOHCH NH2CH2OHH2C OHH2COHSphingosineGlycerol
82SPHINGOLIPID No glycerol – replaced with amine alcohol = Sphingosine Number of carbon atoms –variesThe simplest = ceramides = Fatty acid + sphingosine through amino group via amide bondSphingomyelin – an example of sphingolipid - 1o alcohol esterified to phosphate amino alcohol (= choline)Found in nerve membranes and brain
85GLYCOLIPID When a carbohydrate is attached to OH- via glycosidic bond Seb. induk = ceramide (sphingolipid) + CHOCerebroside - CHO = glucose @ galactose glucocerebrosideGANGLIOSIDE – ALSO contains oligosaccharide + sialic acid
90STEROL Hydrocarbon chain (C18-C20) at C17 ii. Hydroxyl group (OH) at C3Main example = CHOLESTEROL – structural component of membrane % lipid membrane. RigidPrecursor of bile, sex hormones, vit. D.Role in atherosclerosis
93TERPENE Lipid derived from isoprene Term used for all compounds synthesized from the precursor isoprene cholesterol, bile acid, steroid, lipid soluble vitamins = terpeneOils from turpentine (pine tree extracts)formula C10H15> 15 carbon atom also found - `multiples of 5Also in other plants
98PRINCIPLES OF BIOCHEMISTRY BCM 3000PRINCIPLES OF BIOCHEMISTRY(Semester /12)
99LIPID BEHAVIOUR IN WATER Lipid – not soluble in water but can still be found in aqueous environmentbehavior in water important to understand the phenomenaA lot of lipids are amphiphyllic = havinghydrophobic part (hydrocarbon chain)polar (ionic) part
100When lipid is dispersed in water, the hydrophobic part will segregate from the solvent through `self-aggregation' – formmicelles – which are dispersed in watermonolayers ( aggregate – boundary H2O: air
102The tendency for hydrocarbon chains to distance away from polar solvents gives rise to = HYDROPHOBIC EFFECTMost lipids will form micelles – spheres, ellipse, discs, cylindersAlso can form vesicles – bilayer – hydrocarbon chains are opposite to each other `hollow sphere'
105Cholesterol does not form micelles ?? Not amphiphatic compoundsStructure – flat fused ring - solid –difficult to form micellesCan form mixed micelle with amphiphatic lipids mixed micelles – with amphiphatic lipids
106BILE ACID AND BILE SALTS Bile acids serve many functions.They aid in fat absorptionBile acids are produced from cholesterol in the liver.Cholesterol is converted to the carboxylic acids cholic and chenodeoxycholic acid, which are the primary bile acids in most species.The liver conjugates the acids to either glycine or taurine and subsequently secrets them into the bile.The gall bladder serves to store bile acids until contraction associated with feeding
108LIPOPROTEIN STRUCTURE Particles that contain lipid and protein bonds = not (non-covalent) bondsFunction – In blood plasma – to transport triacylglycerol and cholesterolSTRUCTURE- form `micelle like particles' -i. core – non-polar triacylglycerolii. Surrounded by a layer of amphiphilic protein, phospholipid and cholesterol
109Various categories – depending on the functions CHYLOMICRON – Carries exogenous triacylglycerols & cholesterol (from diet) from intestine to the tissues.LDL, IDL & LDL – group of related particles which carry endogenous triacylglycerols & cholesterol (produced internally) from the liver to tissuesNB: liver can synthesize triacylglycerol from excess carbohydrate
112LDL, CHOLESTEROL & ATHEROSCLEROSIS Important component of membrane – can be supplied from the outside or internally (if not enough)How obtained externally ? – ENDOCYTOSIS – Through reaction of specific receptors = LDL receptor?protein part of LDL tie up to R-LDL in the cell complex `pinched off' = endocytosis
115HDL Oversupply ? – Protein – recycled – used in the cell Synthesis of R-LDL inhibited low LDL cholesterol level in blood increases deposited in the artery heart disease; strokeHDLFunction opposite of LDLCarries cholesterol from tissues - extract cholesterol from membrane – change to `cholesteryl esters - LCAT (Lecithin cholesterol transferase) bile acids